Trace elements are widely used industrially and for medical purposes. Platinum, mercury, cadmium, copper, chromium and zinc are used in the plating industries. Lead is used to make electrodes for batteries and lamps. Compounds of these metals are used as catalysts for making varnish and paint compositions.
Waste waters from mining and public utilities contain dissolved or entrained heavy metal ions. Radionuclides, particularly uranium, plutonium and cesium ions, are representative of objectionable and toxic components of waste waters from nuclear power plants or radioactive waste processing installations.
Disposal of wastes from these industries presents ecological problems, particularly when the heavy metals are in soluble forms. The soluble forms are objectionable because consumption of water, containing soluble species of heavy metals, by humans or domestic animals can result in absorption and accumulation of relatively large amounts of toxic heavy metal compounds in the organs of animals, consuming the contaminated waters. The heavy metal compounds can accumulate in nervous tissue, for example, and cause disorders of the nervous system. There is therefore considerable interest in processes for removing toxic or objectionable heavy metal species from waste waters.
Hallberg, in U.S. Pat. No. 4,354,937, has proposed precipitating heavy metals from waste waters by treating the waters with sulfate-reducing bacteria, particularly Desulfovibrio and Desulfotomaculum. Sulfides of metal contaminants in the water are precipitated and can thereafter be removed from the water.
Kauffman et al. (U.S. Pat. No. 4,519,912) have recited removing both sulfate and heavy metals from aqueous solutions by treatment with at least one anaerobic Clostridium organism and a second anaerobic organism, selected from among genera of Desulfovibrio and Desulfotomaculum. The waste water is contacted with the mixture of organisms under anaerobic conditions. Kauffman et al. (U.S. Pat. No. 4,522,723) have proposed a similar process, using Desulfovibrio or Desulfotomaculum organisms, in a porous matrix under anaerobic conditions.
Stern et al. (U.S. Pat. No. 4,584,271) have recited reducing sulfate to sulfide in a two-step bacterially-induced process, involving Desulfovibrio or Desulfotomaculum, under anaerobic conditions.
Balmat (U.S. Pat. No. 4,200,523) recites removal of sulfate from aqueous streams by treatment with sulfate-reducing bacteria, particularly Desulfovibrio desulfuricans, under anaerobic conditions.
Yen et al., in U.S. Pat. No. 4,124,501, have disclosed purifying oil shale retort water, using Desulfovibrio organisms to reduce sulfate to sulfide. The process contemplates aerobic oxidation of sulfide to sulfate, using aerobic organisms, such as those of the Thiobacillus family.
Baldwin et al. (U.S. Pat. No. 4,519,913) have recited removal of selenium compounds from aqueous solution by anaerobic treatment in the presence of bacteria of the genus Clostridium.
The metabolism of inorganic sulfur compounds by various microorganisms has been the subject of a review article by Peck, "Symposium on Metabolism of Inorganic Compounds, V. Comparative Metabolism of Inorganic Sulfur Compounds in Microorganisms," Bact. Rev., vol. 26 (1962), pages 67-94.
Dean et al. (U.S. Pat. No. 3,674,428) and Fender et al. (U.S. Pat. No. 4,422,943) are representative of references, teaching precipitation of heavy metal ions in waste waters by addition of an inorganic sulfide compound.
It is apparent, from the amount of activity in the field, that removal of objectionable or toxic ionic species of heavy metals from waste waters is of continuing importance in providing water supplies, from recycled waste waters, which are safe for drinking or industrial uses.
It is an object of this invention to provide processes by which toxic heavy metal species can be removed from aqueous waste solutions.